Methods relating to wafer integrated plasma probe assembly arrays

ABSTRACT

A wafer integrated plasma diagnostic method for a semiconductor wafer processing system provides a multiplicity of plasma probe assemblies arranged on a wafer in a planar array fashion such that one plasma probe assembly is located in the center and eight more plasma probe assemblies are located at intermediate positions such that they lie along the radius from the center to the corners; such corners forming four corners of a square box near the edge of the wafer. Method operations provide at each location and in each of the plasma probe assemblies, six possible probe elements having a relative geometrical area such that the assemblies may make simultaneous measurements of both spatial resolution and real time measurement of different plasma characteristics at the wafer surface, such as: D.C. potential, A.C. potential, shading induced potentials, ion fluxes, ion energy distribution, and the electron part of the I-V Langmuir probe characteristic.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Divisional application claiming 35 U.S.C. § 120priority from parent U.S. patent application Ser. No. 09/540,418, filedMar. 31, 2000 now U.S. Pat. No. 6,653,852, entitled “WAFER INTEGRATEDPLASMA PROBE ASSEMBLY ARRAY,” which parent Application is hereinincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to plasma diagnostic methods forsemiconductor wafer processing systems. More particularly, the presentinvention relates to methods relating to wafer integrated plasma probeassembly arrays.

2. Description of the Related Art

In the semiconductor industry, plasma, generally comprising of partiallyionized gas, is employed in etching and deposition processes wherebyfilms are etched from or deposited onto wafer surfaces. In theseprocesses, plasma can be characterized in terms of characteristics ofthe interaction between the surface to be processed and the plasma. Suchcharacteristics, and measure quantities of the characteristics, areimportant in order to control the etch or deposition rate andconsequently, the desired dimension of the etch depth or deposited film.These characteristics include the rate of flow of charged particlesimpinging upon the surface to be processed, the potential distributionof the plasma, the ion current flux, the electron temperature anddensity, and the ion energy.

In plasma etching systems, knowledge of the potential distribution ofthe plasma is useful because the energy with which particles impingeupon the surface to be processed depends upon the potentialdistribution. In addition, the plasma potential determines the energywith which ions strike other surfaces in the chamber. High-energybombardment of these surfaces can cause sputtering and consequentre-deposition of the sputtered material upon the surface to beprocessed. In addition, process uniformity is related to the uniformityof the plasma.

Similarly, the ion current flux is an important characteristic of theplasma generated within a reaction chamber of a semiconductor waferprocessing system. This characteristic generally defines theeffectiveness of the semiconductor wafer processing system.Specifically, the ion current flux affects the uniformity of the etchprocess and indicates potential damage to a wafer. The measurement ofion current at various locations within the chamber is thereforeimportant to characterize the effectiveness of the plasma in processinga wafer.

It is thus desirable to diagnose instantaneously from outside theprocessing chamber the various characteristics of the interactionbetween the surface to be processed and the plasma. Prior art FIG. 1A isan illustration showing a conventional wafer 1 having probe structures 2formed thereon. The conventional wafer 1 consists of a Si wafer with theprobe structures 2 fabricated using three levels of masks such assubstrate contact, metal pad and oxide layer. The wafer 1 is processedusing conventional wafer manufacturing techniques.

Prior art FIG. 1B shows the probe structures 2 in greater detail. Theprobe structure 2 includes a semiconductor substrate layer 4, which ison the semiconductor wafer 1 on which are comb-like structures 6 madefrom metals such as Cu or aluminum and with or without layers ofinsulators such as oxide layers 8. In the fabrication of semiconductorIC's in which advanced MOS devices require multiple levels of metalinterconnections, the size of the comb-like structures is such that theheight of the structure could be less than 0.5 micron and the spacebetween the structures could be less than 0.4 micron wide such that theaspect ratio could be greater than two. The aspect ratio is defined asthe height of the comb-like structure divided by the width of the spacebetween the comb-like structures of prior art FIG. 1B. The presence oftall structures on the substrate of a semiconductor wafer sometimescauses a differential charging of the surface due to the difference inelectron and ion currents crossing the plasma sheath to the closelyspaced structures.

The differential charging of the surface (prior art FIG. 1C) is mostlyindicative of a non-uniform plasma which includes fluctuations in theelectron and ion densities, and also indicates differences in surfacepotentials and charge flux densities. If plasma is non-uniform it isanticipated that the depth of etching or the depth of deposition wouldbe variant across the surface of the wafer. Differential charging alsocould cause oxide damage in semiconductor devices due to differences incharge flux densities. This is very important as plasma is in contactwith smooth and not so smooth surfaces on the wafer.

It is a purpose of the plasma diagnostics to ensure that the plasma isuniform across the wafer surface so that the different processes takingplace in the plasma chamber would result in high yield for the deviceoutput.

Prior art FIG. 1C is an illustration showing a probe structure 2 on aconventional wafer 1. As shown in prior art FIG. 1C, the presence ofprobe structures causes shaded regions 10 where there is chargeaccumulation and unshaded regions 12 where there is no chargeaccumulation. The sign of the charge depends on the surface potential ofthe structure. Local inequality of positive and negative charge fluxesreaching the wafer surface results in a net charge. Local charge-fluximbalances result in circulating currents through the wafer thatgenerate charging damage in gate oxides as in IC process equipment.

This calls for application of sufficient RF power for better gap fillcapability. If the plasma is not uniform across the substrate, then theresulting current imbalance causes a voltage to build up in thesubstrate. This voltage allows the current from the plasma to flow inthe substrate to the gate oxides of underlying MOS transistors. However,application of sufficient RF power could cause damage to the gate oxidesleading to gate leakage or oxide breakdown when the amount of currentexceeds the capacity of the gate oxide.

In general, there are two conventional methods of diagnosing thecharacteristics of interest, a probing method, and an electromagneticwave method. In the probing method, a probe 200 may comprise anelectrode 204 (usually made from metal, prior art FIG. 2A) on a support206 and directly introduced into the plasma 202 to detect the electriccurrent in the plasma, which is then analyzed to determine thecharacteristics of the plasma. The probe 200 is also called the Langmuirprobe. A graph 250 with a characteristic I-V curve 252 (prior art FIG.2B) is obtained by varying the voltage on the electrode 204 andmeasuring the current when the probe 200 is placed in the plasma. TheI-V curve 252 indicates that for a large negative value of the probepotential, all electrons are essentially repelled and only ionscontribute to the current leading to an ion saturation current (Isat).This ion saturation current Isat simply determines the electron densityprovided electron temperature can be determined. Conversely, Isat isalso a product of electron charge, disk surface area and ion flow.

In the electromagnetic wave method, electromagnetic waves (includingmicrowaves and lasers beams) interact with the plasma and the results ofthe interaction are detected. By way of example, a beam reflected fromthe plasma is detected by spectroscopy and analyzed.

The probing method is limited to probing plasma of relatively lowtemperature and density. For plasmas of electron density Ne on the orderof 10{circumflex over ( )}14 cm-3 and above and electron temperature ofa few tens of electron volts and above, the probing method is of limiteduse. The electromagnetic method suffers from being complex and expensiveto manufacture.

In view of the limitations of prior art Langmuir probes and probestructures that are also charge monitors, what is needed is a method ofmaking and using diagnostic tools capable of taking simultaneousmeasurements of plasma characteristics such as uniformity, electron orion flux densities, potentials and ion energy in real time across a widearea of the wafer surface while the wafer is inside of the plasmachamber.

SUMMARY OF THE INVENTION

A preferred embodiment of the present invention includes a method ofmaking an array of electrical probes formed upon an upper surface of asemiconductor wafer. In use, the array of electrical probes providessimultaneous measurement of plasma characteristics in real time across awide area of the wafer surface. The plasma is diagnosed while in theprocess chamber to study characteristics of the plasma as it interactswith a wafer. The plasma may be tested, for example, for beinghomogenous in its electron or ion flux density, potential and particletemperature.

The planar array of plasma probes or the planar plasma probe assemblyarray is connected to the connectors on the wafer through the conductiveinterconnects. The resultant assembly of probe assembly arrays,conductive interconnects and the connectors form a wafer Integratedplanar plasma probe assembly array. The probe assemblies are preferablyarranged in a pattern: one probe assembly in the center and four moreprobe assemblies at intermediate positions such that the four probeassemblies lie along the radius from the center to the corners; thecorners being the four corners of a square box near the edge of thewafer. On the same wafer are located four optional plasma probeassemblies spaced from the existing probe assemblies such that they lieroughly in between the probe assembly at the center and probe assembliesat the corners of a square. Each probe has six possible probe elements.The probe elements are wafer integrated Langmuir probes. The probeelements are, however, made from low impedance N-type silicon and areexposed to the plasma unlike in prior art where the Langmuir probeelements are conductors.

In a method of the present invention, the probe elements are clusteredinto an assembly such that four of the six probe elements are ofintermediate size or medium size, shaped roughly like squares, and arecharge monitors with patterning on them. The structures of the fourmedium sized probe elements have a non-zero aspect ratio. The fourmedium sized probe elements are suitable for patterning in differentways to diagnose potentials due to charge shading effects. The probestructures on the four medium sized square elements are rectangularcomb-like structures, which don't necessarily have identical aspectratio. An important aspect of having a range of aspect ratios for theprobe elements is that it gives an idea in real time as to what aspectratio would cause wafer damage in real time. The presence of probestructures on probe elements determines charge accumulation from thedifference in electron and ion currents as they cross the plasma sheathto reach the plasma structures on the wafer substrate. Such adifferential electron or ion flux from non-uniform plasmas isresponsible for causing charge induced damage in some semiconductordevices. The fifth probe element has an area equal to the four mediumsized probe elements and has no patterning on it. An absence ofpatterning makes the probe a plain probe. The fifth probe element withno patterning is considered to have a zero aspect ratio. The fifth probeelement is considered as a reference Langmuir probe and is exposed tothe plasma for measurements of floating potential and saturated ionflux. The sixth probe element is a plain probe with no patterning on it.Again, an absence of patterning constitutes zero aspect ratio. The sixthprobe element is capable of providing electron measurements. However,the sixth probe element is very much smaller than any probe element orexposed substrate for the reason that in order to perform electronmeasurements, the excess current could cause damage to the probe if theprobe's area is bigger because the probes are essentially made ofconductors. The sixth probe element is a novel addition to any of theprior art in plasma diagnostics as it allows electron measurements alongwith flux, potential and charging damage measurements performedsimultaneously in real time.

While it is important that the geometrical areas of the probe elementsbe such that the probe elements form a probe assembly, it is not arequirement that areas of probe pads be the same for all the probes. Thegeometrical shapes of the probe elements are also not a criticalrequirement for the invention. In the invention, the area of thesmallest probe pad is about 0.25 mm squared while the area of the mediumsized probe elements having square pads is 25 square mm each.

The probe pads, the conductive interconnects and the connectors are allplaced on an N-type silicon wafer. There is also a large area that isnot used for any probing purposes and is exposed to the plasma. Thesevacant areas on the substrate are covered with a low impedance N-typesilicon for the sole purpose of making an ohmic contact easy. The largearea of the wafer substrate also acts a floating reference electrode. Atthe floating potential, the probe collects both the saturation-ioncurrent as well as canceling electron current such that the net currentthrough the probe is zero.

There are also four more optional plasma probe assemblies arranged inbetween the center probe assembly and the corner probe assemblies. Thefour intermediate plasma probe assemblies can be rotated with respect tothe plasma probe assemblies located already at the center and at thecorners of the wafer.

Connections from the probe assemblies on the substrate to connectors aremade on wafer traces. By arranging the connector pads to conform to astandardized mass termination array it is relatively convenient toconnect them using wire bonds to a flexible circuit jumper strip to getthe signals off of the wafer and into external diagnostic circuitrywhich includes an analyzer. The analyzer measures the relative electronor ion potentials and current flows from the charge particle fluxes,energies and impressed voltages. The probe assemblies on the wafersurface measure the plasma charge densities and energies when the plasmacomes in contact in the plasma processing chamber. The local grouping ofprobe array assemblies at nine places allows both spatial resolution andreal time measurement of six quantities: DC potential, AC potential,shading induced potentials, ion fluxes, ion energy distribution, and theelectron component of the I-V Langmuir probe characteristicsimultaneously.

Such an arrangement of planar probe assembly arrays determines electronor ion flux densities, potentials and ion energy in real time across awide area of the wafer surface while the wafer is inside of the plasmachamber. The probe assemblies on the wafer allow six differentmeasurements on the wafer when the plasma is in the charge shaded regionor when it is in the charge unshaded region.

In wafer processing, it is highly preferred that the deposition oretching induced by plasma be uniform because millions of devices getbuilt on a single wafer. As there is need to manufacture more number ofdevices on a single large wafer to reduce costs, it is imperative thatthe process involved be as uniform as possible. The diagnostics fromsuch semiconductor equipment should indicate the quality of plasma overa wider area in the semiconductor process chamber because that wouldultimately determine the device quality.

For a fuller understanding of the nature and advantages of the presentinvention, reference is made to the following detailed description takentogether with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further advantages thereof, may best beunderstood by reference to the following description taken inconjunction with the accompanying drawings in which:

Prior Art FIGS. 1(A)-(C) are illustrations showing a prior art waferhaving charge monitors or probe elements formed thereon and waferstructure having plasma shaded and unshaded regions;

Prior Art FIGS. 2(A)-(B) schematically respectively illustrate a priorart Langmuir probe and the current-voltage characteristic of the probe;

FIG. 3 schematically illustrates a plasma chamber with a planar Langmuirprobe, in accordance with an embodiment of the present invention;

FIG. 4 is a schematic illustration of a chemical vapor depositionapparatus, in accordance with an embodiment of the present invention;

FIG. 5 is an illustration of a wafer with a planar plasma probe assemblyarray, in accordance with an embodiment of the present invention; and

FIGS. 6(A)-(C) are schematic illustrations of a plasma probe assembly,in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An invention is disclosed for simultaneous measurement of shadinginduced potentials, ion fluxes, ion energy distribution, and theelectron part of the I-V Langmuir probe characteristic. The presentinvention makes it possible to simultaneously measure several plasmacharacteristics in real time across a wide area of the wafer surfacewhile the semiconductor wafer is inside of the plasma chamber. In thefollowing description, numerous specific details are set forth in orderto provide a thorough understanding of the present invention. It will beapparent, however, to one skilled in the art, that the present inventionmay be practiced without some or all of these specific details. In otherinstances, well known process steps have not been described in detail toavoid obscuring the present invention.

FIGS. 1 and 2 were described in terms of the prior art. FIG. 3 is anillustration of a planar Langmuir probe 300 in accordance with oneembodiment of the present invention. The planar Langmuir probe 300includes an enclosure 302, a disc-shaped electrode 304 on a wafersupport 306. The disc shaped electrode 304 is positioned next to thewall of the enclosure 302. Preferably, the disc-shaped electrode 304 hasa relatively large surface area S (for example, a few square cm). Thedisc-shaped electrode 304 further includes a rear surface directed tothe wall and coated with an insulating material. The forward contact ofthe Langmuir probe 300 is a conductor, and when placed in direct contactwith moving charged particles found in a plasma, a current is createdthrough the wiring in the Langmuir probe 300. The apparatus of FIG. 3,is specifically for diagnostics of the plasma and so the enclosure 302is preferably a vacuum enclosure that is filled with low pressure gas,such as Argon. Applying a bias voltage to the wafer support 306generates the plasma. To increase the ion impact power on the surface ofthe sample placed on the electrode 304, a radio frequency (RF) generator308 is connected to the wafer support 306. An analyzer 310 connected tothe plasma support measures the voltage across the disc-shaped electrode304.

In the prior Langmuir probe method, a cylindrical probe made ofconductor material is placed in the plasma and the current is measuredwhen a voltage is applied between the probe and the enclosure walls. Inthe present invention, the probe 300 is a planar Langmuir probe madefrom low impedance N-type Silicon employed to determine the plasmacharacteristics. The source for plasma could be a d.c. voltage source,an electrode supplied by a radio frequency generator, an inductivecoupling radio frequency source or a microwave source. The purpose ofthe RF generator is to increase the ion impact power on the surface ofthe processing wafer when the plasma is impinging inside the plasmachamber.

FIG. 4 is an illustration of a plasma processing system, such as a highdensity plasma-induced chemical vapor deposition process system 400,where the interactions of the plasma with the wafer occur inside theprocessing chamber. In such a system, the plasma probes 300 (FIG. 3) areembedded on the wafer itself and characteristics of the plasma aredetermined since the same plasma would interact with wafers duringdeposition or etching as applicable. The process system 400 includes asubstrate 304 positioned on a chuck or a wafer support system 306, aturbo molecular pump 310, a wave guide 312, large magnets 314surrounding a source chamber 316, outer magnets 318, and inner magnets320.

In operation, the substrate 304 rests on the chuck 306 disposed inside aplasma chamber and biased by a RF generator 308. The chuck may be eitheran electrostatic chuck or a mechanical chuck and may be biased by the RFgenerator 308. The turbo molecular pump 310 controls the flow ofhydrogen inside the plasma chamber. The wave guide 312 brings microwaveinside source chamber 316, which is located above the plasma chamber.Large magnets 314 surrounding the source chamber generate a magneticfield that sets up a resonance zone inside the source chamber, where theelectrons gyrate at the frequency of the incoming electromagnetic waveor microwave. As a result, a plasma is generated and spreads into theplasma chamber and onto the substrate 304. Outer magnets 318 and innermagnets 320 are used to fine focus this plasma.

In order to perform diagnostics in the plasma chamber of a chemicalvapor deposition system 400, the wafer containing the planar array ofprobes is introduced into the chamber. Plasma is generated in a waysimilar to what is described above. The forward contact of the Langmuirprobes is a conductor, and when placed in direct contact with movingcharged particles found in the plasma, a current is created through thewiring in the Langmuir probe 300. The enclosure is preferably a vacuumenclosure that is filled with low pressure gas, such as Argon. Applyinga bias voltage to the wafer chuck or wafer support 306 generates theplasma. To increase the ion impact power on the surface of the sampleplaced on the electrode 304, the radio frequency (RF) generator 308 isconnected to the wafer support 306. The plasma characteristic, of thetype shown in prior art FIG. 2B, is obtained by varying the voltage onthe probe and measuring the current when the probe is placed in theplasma. For large negative values of the probe potential, all electronsare essentially repelled and only ions contribute to current leading toan ion saturation current (Isat). This ion saturation current Isatsimply determines the electron density provided electron temperature canbe determined. Conversely, Isat is also a product of electron charge,disk surface area and ion flow. For a more detailed account ofmeasurement of electron and ion parametrics, one can refer to “ElectricProbes for Plasma Diagnostics” by Swift and Schwar (1971) which isincorporated herein by reference in its entirety.

FIG. 5 is an illustration showing a planar plasma probe assembly array600 provided in accordance with an embodiment of the present invention.In that embodiment, the plasma probe assembly 600 in FIG. 5 is providedto include six probe elements (633, 635, 637, 639, 641, and 643). Fourof the six probe elements (635, 637, 639, and 641) are provided asmedium sized probe elements (FIG. 6B) suitable for patterning indifferent ways to diagnose potentials due to charge shading effects. Theprobe is usually on a substrate 660 on which there is probe having alayer of overcoat 658 and metal 656. The medium sized probe elements areroughly in the shape of a square but the shape itself is not soimportant.

As in the prior art shown in FIG. 1B, the probe elements with patterninginclude structures 2 that are integrated with a non-zero aspect ratio.The difference in the isotropy of electron and ion currents crossing theplasma sheath to closely spaced probe structures on the wafer substratecauses differential charging. Presence of comb-like structures causesshaded regions 10 (Prior art FIG. 1C) where there is charge accumulationand unshaded regions 12 (Prior art FIG. 1C) where there is no chargeaccumulation. If the plasma is not uniform across the substrate, thenthe resulting current imbalance causes a voltage to build up in thesubstrate. This is understood in the prior art to be the source ofcharge induced damage. The medium sized probe elements (635, 637,639,and 641 in FIG. 6B) in the invention, essentially, determine the chargeuniformity of the plasma at the bottom of the structures in theprocessing chamber. The fifth probe element 633 (FIG. 6C) is configuredwith an area equal to the four medium sized probe elements (635, 637,639, and 641 in FIG. 6A) and constitutes a large probe element that isexposed to the plasma for floating potential and saturated ion fluxmeasurements. The fifth probe element is provided with and consists of asubstrate 666 coated with a layer of overcoat 664 on which is a metalconductor 662. The fifth probe element is plain meaning it doesn't havepatterning on it. That constitutes an aspect ratio of zero for plainprobe elements. The sixth probe element 643 is provided as a smallprobe, configured with an area of the probe element about 1% the probeelement area of all the six elements combined. The sixth probe element643 (FIG. 6A) is capable of providing electron measurements. The sixthprobe element is provided on a wafer substrate 654 with a layer ofovercoat 652 on which is the conductor element 650 which acts as aprobe. The sixth probe element has no patterning of structures and hasan aspect ratio of zero.

From the above it will be appreciated that the described embodimentsprovide a plasma diagnostic tool capable of simultaneously measuring sixdifferent plasma characteristics on a large wafer area.

While the invention has been described in terms of preferredembodiments, other embodiments, including alternatives, modifications,permutations and equivalents of the embodiments described herein, willbe apparent to those skilled in the art from consideration of thespecification, study of the Figures, and practice of the disclosedembodiments. Therefore, the embodiments and preferred features describedabove should be considered exemplary, with the invention being definedby the appended claims, which therefore include all such alternatives,modifications, permutations and equivalents as fall within the truespirit and scope of the present invention.

What is claimed is:
 1. A method for monitoring a plasma, the methodcomprising the operations of: providing a plurality of plasma probeassemblies, each of the plurality of plasma probe assemblies comprisinga substrate and a plurality of Langmuir probes, each of the Langmuirprobes comprising a larger probe, four medium sized probes, and asmaller probe, each of the larger sized probes having a geometrical areaequal to the geometric area of the four medium sized probes, and thesmaller probe having an area which is one-hundredth the area of all theprobes combined; inserting the plurality of plasma probe assemblies intoa plasma chamber; coupling the plurality of plasma probe assemblies toan analyzer; and monitoring the plasma formed in said chamber with theanalyzer.
 2. A method as recited in claim 1, wherein the providingoperation provides the substrate of the plurality of plasma probeassemblies made from low impedance N type silicon.
 3. A method asrecited in claim 1, wherein the providing operation provides the fourmedium sized probes as patterned probes.
 4. A method as recited in claim1, wherein the providing operation provides all of the Langmuir probessmaller than an exposed substrate contact.
 5. A method as recited inclaim 1, wherein the providing operation provides the smaller probe witha geometrical area of about 0.25 square mm.
 6. A method as recited inclaim 1, wherein the providing operation provides the exposed substratecontact as a low impedance ohmic contact.
 7. A method as recited inclaim 3, wherein patterning on the four medium sized probes constitutesfour different aspect ratios.
 8. A method as recited in claim 1, whereinthe providing operation provides all the Langmuir probes much smallerthan an exposed substrate contact.
 9. A method for making a plasma probeassembly for monitoring a plasma, the method comprising the operationsof: providing a substrate; and mounting a plurality of Langmuir probeson the substrate, the mounting operation comprising: defining theLangmuir probes as comprising a larger probe, four medium sized probes,and a smaller probe; configuring the larger sized probe to have ageometrical area equal to the geometric area of the four medium sizedprobes; and configuring the smaller probe to have an area which isone-hundredth the area of all the probes combined.
 10. A method asrecited in claim 9, wherein the providing operation provides thesubstrate from low impedance N type silicon.
 11. A method as recited inclaim 9, wherein the defining operation provides the four medium sizedprobes as patterned probes.
 12. A method as recited in claim 9, whereinthe mounting operation further comprises mounting an exposed contact onthe substrate, wherein all of the Langmuir probes are smaller than theexposed substrate contact.
 13. A method as recited in claim 9, whereinthe smaller probe configuring operation configures the smaller probewith a geometrical area of about 0.25 square mm.
 14. A method as recitedin claim 12, wherein the mounting operation provides the exposedsubstrate contact as a low impedance ohmic contact.
 15. A method asrecited in claim 11, wherein patterning of the four medium sized probesconstitutes four different aspect ratios.
 16. A method for making aplasma probe for monitoring a plasma, the method comprising theoperations of: providing a plurality of plasma probe assemblies, each ofthe plurality of plasma probe assemblies comprising a substrate and aplurality of Langmuir probes, each of the Langmuir probes comprising alarger probe, four medium sized probes, and a smaller probe, each of thelarger sized probes having a geometrical area equal to the geometricarea of the four medium sized probes, and the smaller probe having anarea which is one-hundredth the area of all the probes combined;providing a first of the plasma probe assemblies located at a center ofa wafer; defining a square box disposed near an edge of the wafer, thesquare box defining four corners; and arranging a first four of theplasma probe assemblies in a pattern, one of the plasma probe assembliesbeing disposed along a respective radius from the center to a respectiveone of the corners of the square box.
 17. A method as recited in claim16, the method further comprising the operation of: arranging a secondfour of the plasma probe assemblies in the pattern, one of the secondfour plasma probe assemblies being disposed along each respective radiusbetween the first plasma probe assembly and one of the first four plasmaprobe assemblies.
 18. A method as recited in claim 17, the methodcomprising the further operation of connecting the plurality of plasmaprobe assemblies to an analyser to enable simultaneous measuring of aset of six different real time plasma quantities.
 19. A method asrecited in claim 18, wherein the six different real time plasmaquantities include D.C. potential, A.C. potential, shading inducedpotentials, ion fluxes, ion energy distribution, and the electron partof the I-V Langmuir probe characteristic.
 20. A method as recited inclaim 17, wherein the arranging of the second four plasma probeassemblies rotates the second four plasma probe assemblies with respectto the first plasma probe assembly and to the first four plasma probeassemblies that are respectively provided and arranged at the center andat the corners of the wafer.